text:
How much can falling down due to a stall influence the angle of attack?
I am trying to understand the af447 incident, more precisely, how a professional pilot having an attitude indicator available failed to understand that the angle of attack was too high. Was it that the angle of attack may be too high at the horizontal attitude, or close to that? As I understand, the aircraft stalled due to pilot error.
Over the longer range it cannot be just a free fall; the air friction would stabilize even a round ball to some stable falling velocity.
Knowing the downward velocity, as well as forward velocity, we can compute the angle of attack for horizontal attitude, and various different attitudes. Seems that if it falls with the same speed as it moves forward, the angle of attack would be 45 degrees just for a normal horizontal orientation. Is this situation realistic?

It doesn't fall at all unless it's stalled.  It can fly just as well in a descent.  The only question is for how long.

Please explain what is wrong with the question. The question is about stalled plane. What do you mean "does not fall at all" ?

Why don't you read the BEA report? Everything about the aircraft attitude, pilot reactions and flight path is explained in details and very understandable. By the way, it falls in the category of accidents.

I missed the word "stall" in the title.  The question was not clear, but your edit has helped.

In AF447 the falling motion most definitely affected the angle of attack. Due to the fact that the pf did keep the stick pulled back for all but the last few seconds of the fall the aircraft was so steep that, although the aircraft was falling at a slight pitch up, angles of attack actually reached as high as 60°.
The descent was so steep that the air was passing over the pitot tubes at such an angle that it was reading below 40 knots, although the plane was moving far faster then that. The computer required that the airspeed be of a certain value to consider the aoa plausible so the stall warning stopped sounding even though the aoa was between 30° and 60° during the fall. When it hit the water the forward ground speed and the vertical speed were both 107 kts.
As far as why the pilot did not realize he was stalled, that's the question of the century. Much effort has been put into figuring that out, and there are numerous things that are at play. But in the end I don't think anyone has come up with a satisfactory answer for that.
If you want to dig into the causes of this crash and get a good understanding of Airbus systems in general I highly recommend this book and it's companion website. The author is uniquely qualified and gives the most thorough explanation yet is not as technically challenging as reading the BEA report.

All of the numbers mentioned in this answer come from the linked book.

Your understanding of the situation is correct: The angle of attack was beyond stall and the aircraft was in a descent which reduces the pitch attitude, so the resulting acceleration felt to the pilots close to that in normal flight.
Now it is important to understand that the aircraft produced lift equivalent to its weight. It was in a steady state - if lift had been too small, it would had accelerated downwards. Let's calculate how big the descent angle could have been: The minimum speed of an A330 in clean configuration is 166 KIAS at the maximum landing weight, which is 396,800 lbs or 182 t. Since the aircraft had just flown for less than four hours, I would estimate that it weighed 205 t at the time of the accident, which makes its stall speed 176 KIAS or 90.6 m/s. In about 3½ minutes it went from 11,600 m to sea level, which gives us an average sink speed of 55 m/s. For a very rough estimate we use the mean between the stall speed at 11,600 m, which is 175 m/s, and the stall speed at sea level: 132 m/s. The resulting angle is 22.5° (note that the flight speed is along the flight path, so you need the arctan of 55 / 132.6). The real value was probably a little lower since the aircraft flew a little faster than its stall speed to compensate for the lower lift coefficient in the stalled state. Modern supercritical airfoils have a very benign stall behavior, and I would estimate that the speed was not much above stall speed. Also, it did not fly constantly at the same attitude, but the copilot released his pitch-up command twice, only to resume it seconds later.
When I use the cited values at the time of impact (107 kts ground speed and 108 kts sink speed), the airspeed is 78.2 m/s. Assuming standard atmospheric conditions, this gives a lift coefficient of 1.48 - way more than any stalled wing can manage. This can only be explained by a strong headwind, of which there is no word in the Wikipedia article. Since the plane was flying through a storm, strong winds should be expected, and then the figures become credible again. Tom's value of 60° sounds very unlikely to me - at that angle the wing produces mostly drag and the aerodynamic forces act at mid chord, producing a strong pitch-down moment which cannot be compensated by a tail surface at those 60°, regardless of elevator position. Around 20° to 30° angle of attack the whole situation becomes much more plausible.

EDIT: Now I spent some time reading the BEA report (thank you @mins for the link!) and are deeply troubled by some details. In FL360 (figure 65) and with 1g (figure 66), the airplane was supposed to have flown at only Mach 0.4. This translates into a post-stall lift coefficient of 2.09, which is physically impossible. Some lift is contributed by the engines due to the positive pitch angle, granted, but by far not enough to make this low speed possible. At least BEA agrees with my mass estimate.
The dynamic pressure at this point is only 2660 N/mm², and in clean configuration this is too little to prevent the plane from dropping like a stone at any angle of attack. The same goes for the condition right before it impacted the ocean surface: 78.2 m/s is too low; at least 95 m/s would be needed for a barely credible post-stall lift coefficient of 1.0. If I add 17 m/s wind speed, things get back into normal territory. Unfortunately, the only wind information in the plots is in figure 64, when the stall begins. Headwind is around 0, but crosswind is between 20 and 30 m/s. If the airplane had sideslipped so badly during the stall, it would had entered a spin. It just does not make sense.
In the text we get a headwind information at the time of the autopilot disconnect (page 91):

Prior to the disconnection of the autopilot, a constant headwind
  component of 15 kt had to be added in order to make the simulation’s
  ground speed match the recorded parameter. This value was consistent
  with the wind parameters recorded.

But the most important line is at the start of the analysis, hidden away at the bottom of page 90. It should be bold and underlined, but isn't:

The validity of the model is limited to the known flight envelope
  based on flight tests.

Airbus did some more flights at the same configuration and loading as AF447 had at the time of the accident, but it appears that buffet limited their flown angles of attack to below 10°.
It must be concluded that all angle of attack values exceeding 10° are purely speculative and not backed by flight test data.

From the BEA final report: "At about 2 h 12, descending though FL 315, the aeroplane’s angle of attack was established around  an average value  of about  40  degrees.  Only an  extremely purposeful crew with a good comprehension of the situation could have carried out a manoeuvre that would have made it possible to perhaps recover control of the aeroplane. In fact, the crew had almost completely lost control of the situation. Up until the end of the flight, no valid angle of attack value was less than 35°. "

@TomMcW: It would be interesting to know how they established those values - are the AoA vanes still calibrated in this range? The flow around the fuselage will increase the readings, and I wonder what corrections were used. I guess I need to reduce flight speed in my back-of-the-envelope calculation a lot to arrive at these values. When I use the values at the time of impact (108 kts), the airspeed comes out at 78 m/s, less than what I assumed.

I can't attest to where captain Palmer gets his 60° figure, they're not that specific in the bea report. But they do include the graphs in the appendix. It appears from the graph that the aoa vane pegs out at 45° It spends several seconds showing 45° while the pitch graph shows up to 15° pitch up. That might be where he is extrapolating the 60° number. It definitely hovers around 40° indicated aoa for the last part of the fall. I can't find an image of the chart that isn't part of a pdf or I'd add it to my answer.

And they do have a line marked "calculated aoa." I'm assuming that is combining forward speed, vertical speed and pitch angle. It seems to be pretty close to what the vane output is showing. It's actually fairly surprising that the yaw damper and the pilots' pitch corrections kept it from going into a spin after such a nasty stall

@TomMcW: Thank you for the details - I have to rely on Wikipedia and sound reasoning. The AoA vanes are at the side of the fuselage, right? You cannot take their readings at face value, but need to factor in the flow around the fuselage which will likely double the local flow direction versus free stream flow. This is the correction I wonder about. Is there any word in your sources how they corrected the AoA vane readings? Were the actual vane angles quite a bit above 45°?

@TomMcW: Also, the speeds at impact are impossible. When I add all forces which hold an aircraft up at this attitude, the coefficient is around 1, slightly less in most cases. The 107 kts speed number must be corrected with a sizable wind speed, or the numbers don't add up.

The graphs are, unfortunately given without explanation. It doesn't say exactly how they arrived at the "corrected" aoa figures. I'm presuming that it is what the fdc computes to correct aoa but I don't know that. Being that the fdc is not programmed for such unusual regimes it wouldn't be surprising if it's off.  There are three aoa vanes located on the sides. IIRC two on the captain's side and one on the FO side. How sizeable off a wind speed would be needed to come up with their figures? They were in a pretty strong storm at the time.

Regarding the unphysically-low speed, keep in mind that the airflow into the aircraft's pitot tubes would be severely impaired at extreme angles of attack, causing the airspeedometer to read falsely low.

@Vikki-formerlySean: Agreed, but why does the report neither apply a correction or even point out that the readings are false? Again, deeply troubling. I had hoped that of all people the authors of this report would apply some common sense and basic knowledge, but no, they let impossible numbers stand uncommented.

@PeterKämpf: Maybe they thought that it would be obvious enough to the sorts of technically-knowledgeable people who would be digging that deep into the nitty-gritty of the report to not require explanation?  (Not saying that that was the right thing for them to do; just putting it out there.)

You are exactly right that the pilot should have noticed he was in a stalled configuration due to (among other things) that the attitude indicator would be showing nose up.
Your guess about a 45-degree down angle is not quite right. That would cause a large increase in speed and constitute an uncontrolled dive. Not good, but definitely better than stalling.
If you pull the nose up and hold it there, then what happens is that the aircraft loses speed steadily until it stalls, then it falls rapidly. In a semi-stalled condition (what occurred to the AF447 flight), the aircraft will be buffeted from side to side as it slides to the ground in a nose up configuration. When this happens the controls become "mushy" and the aircraft becomes difficult to control. This happened to AF447 and that alone should have told them they were stalled.
When there is no visual horizon and the pilots are flying blind it is easy to ignore or misinterpret the controls or focus on the wrong instrument. The pilots involved simply failed to realize they were stalled. The problem was compounded by poor command skills. Normally only ONE person is allowed to have the controls and that control can only be switched using an explicit protocol. The pilots of AF447 were not obeying this rule and both pilots were working the controls at the same time. The response of an Airbus to this behavior is to average the two inputs. Obviously this created more confusion.
One additional issue with the A330 is that it has what is called a "supercritical" airfoil shape to its wings which give it poor stall recovery characteristics, especially when fully loaded. When they tested the A330 in a simulator using the same conditions as in AF447 it took an expert pilot 23000 feet to recover from the type of stall they were in. So, once they had fallen below that altitude, they were dead and situation was unrecoverable.

Sorry, Tyler, but the springs in the sidestick don't get mushy in a stall. This is not a Cessna, and all control feel is artificial. I agree that in a mechanical control system you can feel the stall with stick forces alone, but not in a FBW aircraft. And I would not trust an airliner simulator with simulating the post-stall behavior of the aircraft.

@PeterKämpf I was speaking metaphorically. In the case of a fly-by-wire aircraft, what happens is you make an input and aircraft does not respond, or responds slowly or partially.

Not very, I'm afraid.
First of all,it is the angle of attack (once it goes beyond a certain value) that influences (causes) stall and not the other way around.
You're correct that any body will reach terminal velocity while falling through atmosphere. But the stalled aircraft is not a free falling body- the engines are still producing thrust.
Another thing is the stalled aircraft rarely falls like a stone- the pilot is trying to regain control; the aircraft usually rolls or enters into a spin. Depending on the condition, the nose dips, decreasing the angle of attack. The only way for the aircraft to follow a trajectory described by you is if the pilot is holding the wing at a stalled attitude the whole way down.
Even in a (highly unlikely) case where the aircraft falls so that the horizontal and vertical velocities are the same, it will be the trajectory that will be at $45^{\circ}$, not the angle of attack, which can be any value be over the stalling angle.

But as you are starting the stall the forward flight surfaces will stall before the rear ones and lead to a pitch down moment.

@PeterKämpf I think by trajectory, he means relative to parallel with the surface rather than relative to the wing chord line (as AoA would be.) At least that was the way I read it. Obviously, the angle of the flight path relative to the surface is not always (and usually not) equal to the AoA (or the opposite of the AoA, as the case may be.)

@ratchetfreak: Modern FBW airliners with relaxed stability will not pitch down so reliably, and their supercritical airfoils show little lift drop through the stall. You need to pull more per degree of angle of attack to increase the angle of attack further, but can trim the aircraft in a post-stall condition. That is exactly what happened: The pitch-down moment caused by the stall was small and easily overpowered by full stick aft.


text:
What are the benefits of mounting an engine above the fuselage?
I'm wondering what advantage/disadvantage, if any, does mounting an engine above the fuselage give? This question comes up after seeing the Macchi M.33 below:

The engine mounted in such a way does look interesting, but I'm wondering if it might make the plane want to dip down slightly. Any help would be appreciated.

I suppose you mean, other than the obvious one of keeping the propeller out the water and spray?

Clearly, yes. But I'm talking about benefits to flight.

Given that you only see this configuration on seaplanes you may want to ask what the drawbacks are.

@GdD The Boeing 727 wasn't a seaplane, and it had one of its engines in a similar position.

Not really @nick012000, on the 727 it was far closer to axis of the airplane.

@nick012000, don't confuse the intake with the engine:  The middle engine of the 727 was about as far above the axis as the F-16 engine is below.

It's strictly to stay clear of spray in seaplanes, or because the engine was tacked on as an afterthought for some reason (like a motorglider conversion) and that was the only place to put it.
There aren't any aerodynamic benefits, or you would see the configuration on landplanes.
You've increased the frontal area by having a big pod sticking out.  The high thrust line wants to pitch the airplane over, increasing tail trimming forces required to compensate, and hence drag. There there are the undesirable handling qualities, mainly a strong pitch down tendency when you add power quickly, and worse, a pitch up tendency when you remove power quickly, which can get the unawares into quite a lot of trouble.
So to summarize, sticking an engine there is only done when there's nowhere else to put it.

"There aren't any aerodynamic benefits, or you would see the configuration on landplanes." The Boeing 727 has one engine like this.

No the engine is in the tail cone.  The intake is an S duct.  The DC-10 is closer to your point, but the engine is right on top of the fuselage, not sticking way up on a pylon in order to clear a propeller.  Irrelevant for the purpose of the question.

It's still mounted above the fuselage, which is what the question's about. It's not as far above the fuselage, proportionally, but it's still above it.

@nick012000 A better example would be the Heinkel 162. But the last sentence of the answer sums it up nicely and applies to all examples.

“There aren't any aerodynamic benefits, or you would see the configuration on landplanes.“ Non-sequitur. It could conceivable be that there are benefits, but only small ones that are outweighed by disadvantages of safety, maintenance etc..

@PeterKämpf note that we're talking about placing the engine several feet above the fuselage as in the OP's picture. In the case of the 162, it's still sub optimal, but the pitch effects of the only slightly elevated thrust line is much milder, and I have read that the 162 had pretty good handing qualities considering its squirrelly appearance. The CRJs I flew had slightly above the CG thrust lines and there were detectable trim changes with power if you were observing. On the case of the DC-10, the tail engine would be beneficial in countering the pitching effects of the wing engines.

@leftaroundabout If you had an airplane with the engine in a more ideal location, and asked if there could be any aerodynamic or behavioural improvement moving it to the top of a pylon several feet up above, I can tell you that the answer is no, nada, nothing, zip, waste of time.  The expression "you would see the configuration on landplanes" is a practical proof that a 100 years of designing agrees that that is the case.  Same as with canards.  If they really were superior, after all that promotion by Rutan, they would be everywhere, not an oddity.

@nick012000: WRT the 727, DC-10, and similar, the problem that tail-mounted engine is addressing is where the heck are you supposed to stick a 3rd engine?  Regulations meant you had to have at least 3 for over-water flights, 4 got you into size & cost territory.  So you traded off the disadvantages of things like S-ducts and more complicated tail structure for the advantages of the 3rd engine.

@nick012000 - better examples for the point you're trying to make would be the DC-10 or MD-11, where the third engine actually was mounted above the fuselage, as part of the vertical stabilizer structure. However, in both the 727 and L-1011 the third engine is mounted fore-and-after inside the the fuselage and an S-shaped duct is used to supply air to it.

I'm surprised I haven't seen the A-10 mentioned here. The reason for the high-mounted engines isn't because there's nowhere else to put them, nor is it for ground clearance.

@CareyGregory The post is about engines placed WAY above the fuselage, on pylons meant to clear propellers, mostly on seaplanes, not jet engines and turbofans engines mounted slightly above at the tail.  The A10 isn't much different from any business jet like the Challenger (which has the same engines) where the engines are slightly above the vertical CG and aerodynamic center.

@JohnK Okay, but I didn't see that much specificity in the question. It seemed quite broad.

@CareyGregory: I believe the reason for the somewhat high placement of the A-10 engines on the fuselage is to allow the tailplanes to help hide the infrared signature of the exhaust from ground-fired missiles.

Many light-sport airplanes and ultralight airplanes have a high-wing configuration with a high-mounted pusher engine behind the pilot.  Here the engine is above most or all of what one would normally define as the "fuselage", including the tail boom.  One advantage of this configuration is that it gives the pilot a more unobstructed view in the forward direction.
Examples:
Challenger ultralight
Bailey-Moyes Dragonfly
Sportflight Talon
MX Quicksilver

These configurations have the wings as main drag source in line with thrust, and hence avoid the the pitch-down torque of the M.33 in the picture. Plus, design criteria in Ultralights are really different to "normal planes" (pilot positioning affects cg a lot, focus on forgiving flight behavior over aerodynamic efficiency .. )

Again, these aircraft have engines SLIGHTLY high, not way up on a pylon.

The main purpose is, of course, avoid that the propeller hits the water (or ground).
In the other hand the thrust is applied above the CG point of the aircraft. This introduce a considerable moment arm that, translated in manovrability, means an unwished tendence of the plane to dive when the power is suddenly increased.
So we add a little pitch angle up on the engine pod.  Because the prop is forward of the CG, this helps counter-act the nose down torque of the high mount when thrust is applied.
The advantage is to counter-act the tendency of a plane to climb when thrust is applied.  Many aircraft have down thrust angle even when the motor is mounted in front of the fuselage near the center of gravity, rather than above it.
In design, this plane is essentially a low wing PBY Catalina.  Amazingly, it was bested in the 1925 Schneider Cup races by two biplanes: the Gloster IIIA and the Curtiss RC3-2 (flown by none other than Jimmy Dolittle).  It could not be raced at full throttle due to wing flutter issues.
Macchi would go on to set a speed record for all piston aircraft with the M.C. 72 at 440 mph in 1934, a record that would stand for 5 years.

No need for the usual floats.
Floats obviously add both weight and drag so it is beneficial to fly without them. With the fuselage sailing like a ship, they are not required. There are some under the wings but tiny. They do not support the full weight of the aircraft.
But floats also keep the aircraft in expected orientation, raised above the water, same as it would be raised above the ground. Without them, the traditional place for the engine is just too low.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

authors: Bob Jarvis - Слава Україні

sort: votes


text:
Why does the B-29 have eight oil needles?

In the image above, quiet flyer and I realized that there are 2 needles in every oil gauge, and there are 4 oil gauges. Well, why in the world are there 8 needles in total? And the optimal range arcs and redlines of each oil gauge is different. Why would that be? Oil is oil, I can't see how the optimal range arc for some oil in one gauge is different from the optimal range arc for some oil (same oil, oil is oil, the B-29 does NOT run on multiple oils. It isn't an eco-plane and it drops bombs. It has no need for more than one oil) Any thoughts would be great. Solving questions concerning something like dials and maximum speed with flaps extended for such an old plane have answers that are hard to come by, since they would have had to note this stuff down on paper and not electronically, and the people who built them are either very, very old; or unfortunately dead.

The image is of the Flight Engineer's "Wall of Dials", from the "Bockscar" B-29, the one that dropped Fat-Man (I think). Unfortunately there is some visible wear and deterioration on the panel and as a result, there are many painted Warnings, settings, etc. that have worn away and only a few letters remain.

There are also two fuel pressure gauges, with different color ranges. Presumably they're measuring at different points in the fuel system. This also gives us a clue what might be going on with the oil pressure gauges. But I don't know any specifics.

https://airpages.ru/eng/mn/b29_16.jpg

There is more than one type of oil in the b29, hydraulic oil is used for the braking system...

"It has no need for more than one oil" SpaceX employee detected. (spaceX is on a crusade to eliminate all redundant fluids on rockets,

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
FAA Aircraft Registration Form AC 8050-3 doesn't exist
I am preparing to certify a self-built aircraft as flightworthy and legal to fly, and was reading the required documents listed on FAA's Amateur-Built Aircraft Airworthiness Certification page when I realized that FAA does not have the required document "AC Form 8050-3" when searching the form on the FAA Forms website. Is this some kind of mistake? Or is the form possibly a form located inside of a larger form, which could explain why it isn't showing up (Because if that were the case, it wouldn't be its own individual file)? If anyone could provide a link to this form, that would be great.

That's because 8050-1 is the Aircraft Registration Application, and 8050-3 is the Certificate of Aircraft Registration.
You submit 8050-1, and the FAA sends you 8050-3.

Now you got me curious to what 8050-2 contains.

@Mast According to a short Google search, it's the "Aircraft Bill of Sale" to prove ownership of an aircraft.

@Mast UFO records.


text:
Did WW2 airplanes ever jettison their empty external fuel tanks to act as weapons?
Jettisoning an external fuel tank over a populated area is prohibited by the FAA as it will almost certainly cause injury and damage to the people in that area.
But did war airplanes during World War 2 ever use that fact to their advantage?
As an example, say a P-51 Mustang dropped its bombs onto a city/town as a part of its mission, and then they realize that their external fuel tanks are empty, and are ready to be jettisoned. Well, couldn't the P-51 just jettison the external fuel tanks over the city/town to cause some additional damage?
So, did war airplanes during World War 2 ever actually jettison their empty external fuel tanks over bombing targets to cause additional damage?

Yes, and not even empty tanks. It didn’t always work, but it’s happened:
     This is how American pilots used drop tanks as bombs during WWII.
Fun fact, cellulose drop tanks were developed to save metal during the war! The article references P-47s, but I would not be surprised if P-51s did the same.

I clearly recall reading about the "Flying Tigers" using the drop tanks of their P-40s in this fashion.  I don't recall whether or not  the account specifically said that they had to go back and fire at the impact area w/ their guns to cause ignition.  And whether the account I read was actually true-- who knows, unfortunately I can't recall the source--

Btw, regarding the link referenced in this answer -- P-47s did not actually have "cannons", only 50-caliber machine guns.


text:
How is it proposed to preflight check the elevators and gear tabs on a McDonnell Douglas MD-83?
Ameristar 9363 had a runway overrun due to faults with the gear tab on the right stopping that elevator from rising so the plane get not get off the ground. NSTB investigation recommended preflight checks on the elevator and gear tabs. How is this proposed to done given they are indirectly controlled by the control tab and requires airflow and it is 9 meters above the ground?

Somebody has to go stand under the tail and confirm that the gear tabs are working when the stick is moved.  The airline would probably do that on the Daily Inspection in the morning. The elevators would just hang there, but you would want to make sure they are both fully down.

@john k As I understand it the geared tab doesn’t move unless the elevator moves. I’m pretty sure this question has been asked before and never got an answer.

@TomMcW Depends on what it's doing.  Manually operated elevators often use geared tabs to lighten forces, where you drive the surface and the tab moves in a sympathetic direction to help.  DeHavilland Canada used these a lot, with the elevator itself driven by a torque tube spring that was linked to the geared tab.  A small movement would mostly displace the spring tab as the torque tube twists under load and start the surface moving.  A harder input would start to transmit force directly to the elevator.  On the  DC-9, the stick only drives the tabs and the elvs just trail in the breeze.


text:
How do airports manage gate assignments for aircraft?
Today, some companies like Delair, SITA and INDRA provide airport Resource Management Systems (RMS) for gate allocations, which show information as a Gantt Chart.
I know that air traffic controllers use a flight progress strip to track flights under their control, but how was parking managed in the past without today's RMS solutions? What do dispatchers use for gate management? If it's manual, what is the process?

Aircraft stands are usually assigned by the airport or a handling agency, not air traffic control

you're right , thank you for correcting my mistake.

@J.Hougaard I think the word "controllers" in the question include all personels guiding the airplane (from en-route ATC to "follow-me"cars, including people managing airort ressources)

Before resource management applications, it was possible to use paper T-card planners like this. Factories, hospitals, schools, mechanics, etc have used it (and still do), so why not airports?

Your verb tense is a little confusing because you are asking in your first question for what was used, and in the second, you are asking for what do they use.

Depends on the airport. Some airports assign blocks of gates to specific airlines, and they then assign them to flights (usually on an as-needed or first-come-first-serve basis).
Other airports assign them all themselves, again usually on an as-needed or first-come-first-serve basis.
Of course there are categories of gates as well, size and capacity determine what aircraft types can be handled by specific gates.
In theory at least, and no doubt small airports do it that way, it can be handled all with pen and paper. Larger airports of course will have some sort of computerized system for it, either purchased off the shelf or something they had custom built for them.

Most airlines or airports (if they control gate allocation) have their own software to do this. It's based on all the usual variables (gate aircraft type capacity etc.). I'm aware of one that prioritises certain flights based on distance to expected take-off runway (to minimise taxi time), but it's a standard optimisation problem solved using software. If the process is manual, it's based on the heuristic knowledge of the dispatchers ie. can seem a bit random, but works! I was always amazed at the skill of the 'ops' guys when they did the gate planning manually. They managed to squeeze everything in perfectly, but it was not something they could explain as a process: just something they knew how to do after years of experience.

One more intersting rule I came across in gate allocation software for an airline's own terminal: flight block time. Shorter haul flights were allocated to gates closer to the operational runways - the idea being that long haul flights had the capacity to make up time after a longer taxi. An extra dimension to this rule was a 'arrives at slot controlled airport' flag. If this is true, the aircraft were allocated closer to the operating runway, to minimize the risk of missing a slot. It all ends up being quite 'black boxed', but seems to work - although the plans required 'massaging' manually.

Depending on the airport, an airline may lease gates(s) and have exclusive rights to manage that particular gate or parking location. Typically there is always common use gates, which are allocated based on advance schedules submitted to the airport authority for approval.
Gate management software is often used.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How is this rotor setup flying?
I've been researching about helicopter flight without a tail rotor and the closest I've found is intermeshing rotors or this: https://www.quora.com/Why-dont-helicopters-have-rotor-blades-at-the-bottom
Looking at this new method:
Seen in this frame, the rotors are single winged and I'm guessing they rotate at opposite phases. What is this called and where can I find more information about it?

You are right, the two rotors move in opposite direction. This is called a co-axial rotor and is used by the Russian helicopter design bureau Kamov. A co-axial rotor can also be found on many model helicopters for indoor flying. They are a subspecies of helicopters with contra-rotating rotors.
Helicopters with contra-rotating rotors do not need a tail rotor and are much easier to fly than Sikorsky-type helicopters, because they suffer much less from instability. This group also comprises intermeshing rotors like those used on Flettner or Kaman K-Max helicopters.

Kamov Ka-32 with co-axial rotors operated by HeliSwiss (picture source)

Kaman K-Max with intermeshing rotors modified as an unmanned vehicle (picture source)
For more info, just follow the links.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What is this aircraft that has flown over my house all day?
I mainly joined to ask this question. I would not have been so curious had it not flown directly over my house at least 5 times in about a half-hour. Every time my house started rumbling, I’d rush outside to snap some pictures before it was too far gone. Any help would be appreciated - especially if anyone knows why it came across so frequently.

I wish i had a house under some c17s

I disagree that this question is a duplicate. One cannot search based on just an image on SE, you can only search text. Given that a person asking to identify an aircraft inherently does not know the name of the aircraft, how can they be expected to find a previous post asking about a C-17?

If you want to know why it's flying over your house, it would help if we knew where your house is located :-)

Looks to me like a Boeing C-17, if you live near a military base or airport that may explain it.

Beat me to the punch.  It is indeed a C-17 Globemaster.

As its gear is down, it's likely flying circuits, short flights, or touch and go landings at a nearby airfield.

Thanks all! Very interesting. I did some research and they first started in Charleston, SC. Makes sense since I live in South Carolina.


text:
What are U-2 loiter and stall speeds at low altitude?
I've read that a U-2's takeoff speed is around 115 mph (or kts?). Given those glider wings, how slow could one fly, lightly loaded, at low altitude? Say, less than 10,000 feet?

A copy of the flight manual was released under a FOIA request and can be found here. It actually does not say a whole lot about stalls but it does reference some minimum speeds in the emergency engine out procedure section under "COMPLETE POWER FAILURE IMMEDIATELY AFTER TAKEOFF"

Maintain a safe flying speed and control until contact is made

NOTE: The following minimum safe speeds (10kts above stall) are recommended for the accompanying take off fuel loads
...
Fuel  |      Min Speed
...
685 | 90

So at ~runway altitude lightly loaded the plane could fly as low as 90Kts which is 10 Kts above the stall speed which is in line with other answers here. (Operations Manual Page: 3-3). At full fuel the stall speed rose to ~105Kts.
The manual devotes a whopping 2 paragraphs to stalls and lists no performance figures for them in section 6.
Strangely (or perhaps not so strangely) the the document lists an "Appendix I" which should contain the Operating Data (performance figures) but is absent from the document and regrettably where you would find the true answer.
Keep in mind this is the Handbook from March 1st 1959 and there have been several variants since so the numbers may vary.
Note the takeoff speed for a lightly loaded U2 was indeed 95-100Kts (Operations Manual Page: 2-12)

Thanx, Dave. Close enough: I will assume that the swing-wing wing-extension space planes I'm designing as backstory for Sci-fi could loiter at 90 Kts. lightly loaded, 120 or so with a full load.
JO


text:
Can static electricity affect navigational instruments?
Is it possible for navigational instruments to get affected by static electricity or electrical discharges like lightning? If so, how does this happen?

What kind of instruments are you talking about? Complex computers like the ones of an Airbus? Or rather basic instruments like the ones in a GA aircraft?

@Madhav welcome back after a long long break...

As a historical note, ADFs receiving NDB signals are typically no longer used for enroute navigation, but when they are, lightning makes it difficult since the ADF needle swings toward a lightning strike rather than staying pointed at the NDB station.

What do you mean "rather basic"? Our GPS/NAV/COM units are pretty complex too.  Mine is actually marketed as a Flight Management System, and can do everything the big boys can do.

This will depend on the system, but the over all answer would be Yes at least to some extent. When talking about VOR/VORTAC/DME/NDB/GPS or any other nav system that relies on both a device in the plane as well as a device elsewhere we must consider how these devices talk. In this case we are talking about radio waves (em propagation), and lighting does produce an EM field so it has the capability to interfere.
That being said "interference" has both a technical term and a reality IMO. On paper, yes this may interfere with the signal but in reality lightning is fast and isolated so its momentary interference may not interfere with the operation of the device over a usable amount of time or may cause a momentary drop out.
Local INS (Inertial Navigation Systems) if you have it would remain generally unaffected.
There is another issue that presents itself if the lighting is very very close to the aircraft and will be more of an issue with composite aircraft. For what it's worth, if the whole skin of an airplane is conductive (as with metal skinned aircraft) it will act as a pretty solid Faraday cage. This will vary from plane to plane but is generally true. Thus if the lightning generates a strong enough EM pulse the interior of the plane will be protected from it. On a composite based plane you potentially expose yourself to flux related power surging. It should be noted that the critical electronics are protected from this kind of damage.

ADF receivers just point to the strongest RF signal at the frequency that they are set to.  I've seen them swing and point to a thunderstorm.  I've even read of intentionally setting to a non-used frequency and then using the ADF receiver as a "poor-mans" Stormscope.
Just don't follow that needle into a storm!

Before , I answer this question, I would like to elaborate that navigation instruments can broadly be classified into three
 1. Radio Instruments
 2. Pressure Instruments
3. Gyro- Instruments
Radio Instrument are only instruments effected by the static electricity. Radio instruments work on radio signals , which are electromagnetic in nature. Static electricity interacts with the electric components of the signals , hence static interference is there. However, VHF and above frequencies are not effected by the static electricity. Wick discharges , hanging at trailing edge of the wings , are being used to get rid of static electricity


text:
Treated for Anxiety During Pandemic - can I get 3rd Class Medical
I started doing my dual instruction recently, as I am pursuing a Private Pilots License.  I have begun researching the medical that will be required, and had a couple question I was hoping to get opinions on before moving forward.
I'm a bit of a hypochondiriac, and during the Covid-19 pandemic, I began to experience some severe anxiety surrounding my health.  I went to the doctor, and he said I have generalized anxiety disorder and panic disorder, because I experienced a few panic attacks while laying in bed. I began treatment with Prozac, and ceased taking it approximately 4 months ago (9-10 months total).  I am back to normal now, but if I login to my account with my doctor, it still has Generalized Anxiety Disorder and Major Depressive Disorder listed. Concurrent to these diagnoses, I obtained my college degree and handled high stress situations as a D1 athlete, so it obviously isn't affecting me in any way that would be detrimental to aviation. Will this cause any problems for me, and if so, is there anything I should do before mentioning it to my flight instructor and getting my medical to ensure it goes as smoothly as possible, such as going back to my primary doctor and asking to be classified as cured? I have already sunk substantial time and money into this endeavor, and would be crushed if a technicality such as this would hold me back.
(I read similar threads on this forum, but felt none addressed my specific circumstances, so I am creating a new thread)
Thanks, Gary

Please add what jurisdiction you are asking about. The general advice on here though, is to go to an AME as a consultation before applying for a medical.

I am in the United States.  Thank you for your reply.  I appreciate the advice and will look into the consultation as you mentioned.

What @TomMcW said is excellent advice. Talk to an AME first, make sure you make it clear you are not applying for a medical, you just want an opinion.


text:
How do splayed wingtips work?
I need to know more about the "splayed wingtips" design made by Airbus in their latest conceptual design "birds of prey".
How would wingtip vortices work on this plane? How are they reduced by the splayed wingtips or the feathered tips?

Welcome to Stack Exchange! I hadn't heard of this design before this post, so you may want to provide a link. I found this one on twitter.

You may also provide a picture/drawing of such design.

Do we even know they work? Airbus (and every other aircraft company) tends to show many concepts just for the PR and publication count. The designers may not yet know how useful it would actually be, or may even be convinced it's a complete nonsense, but publish it anyway.

The basic idea is to try to extract as much of the available energy in the tip circulation as possible, and it's thought that soaring birds like eagles have this bit figured out.  What it is in essence is an array of winglets.
You have a spiral flow field circulating around the tip, with the most intense part of it near the center - the tip vortice - but there is a circulation flow extending well away.  The flow, being a tip circulation, is not coming from the "normal" direction that the rest of the wing sees.  You can exploit this by sticking airfoils in spots were the local flow allows the lift vector to be beneficially exploited because is it canted forward somewhat (lift and/or thrust), as well as creating a local "downwash" that tends to oppose the circulation, effectively weakening it.
A single vertical winglet, the original concept, does this by creating a thrust component by the lift it generates in the circulation (horizontal toward the fuselage, but also with a forward component - thrust), as well as an "outwash" that opposes the circulation.  Because it's vertical, it's not making any vertical lift and doesn't add to the wing bending and doesn't add to the span dimension.  It's a sail, like on a boat, making thrust as well as redirecting the circulation back in the other direction, and in fact winglets were originally called "tip sails".
It's kind of a "well, if one works, why not add as many as I can" kind if idea.  I can add more winglets if I want at different angles; some will be making some vertical lift depending on how horizontal they are - more or less acting like added span, some with a more vertical orientation will be making mostly "thrust".  All are trying to extract energy from this circular flow, that is normally wasted, creating extra lift and/or thrust depending on the exact location and orientation.
Like winglets, these kinds of devices generally are only worthwhile when airplanes cruise at higher lift coefficients where the circulation is strong - that is, low indicated airspeed.  To get that condition, you need to be above 30000 ft, more or less.  This is why winglets are rare on turboprops and piston airplanes - they don't do that much good, except maybe enhance climb performance.
None of this stuff is new (aside from things related to jet propulsion, most things in  aviation had been already tried by about 1940).  I'd be surprised to see this sort of thing on a turboprop because it would only really work at low indicated speeds, and turboprops cruise at high indicated speeds. But maybe Airbus is on to something all new - who knows.

Splayed wing tips are like .... Fowler flaps.  Totally useless for cruising flight unless .... you want to try the "coffin corner" at perhaps 60-70,000 feet.  The best wing for cruising remains the high aspect albatross style.  However, they may wish to fold them back in cruising flight.
The writer had imagined this for the Etrich Taube.  Unfolding them on approach would greatly reduce the probability of tip stall and make lots of drag.  Strictly a low speed gimmick.  (By the way, slats also do this very well, actually helping high AOA pitch control).
However, the design does hold some interesting concepts:  no vertical stabilizer AND a high wing mount.  Sort of a fuselage mounted on a flying wing with an Hstab for better control.
These concepts, along with engine mount location, bear further study.  The rest is for the birds.

"How would wingtip vortices work on this plane? How are they reduced by the splayed wingtips or the feathered tips?" If you meant they work like Fowler flaps, can you also address the wingtip vortex question, which is not present on the flaps?

@AEhere well, if you put the Fowler flaps at the ends of the wings (along with slats) it would be awesome (but unneccesary).  At higher speeds (that the albatross flies) these structures are not needed (possibly because the vortex is shed more to the rear).  The Etrich Taube wing maybe a good starting place for this project.  Splayed wingtips are excellent for very slow flight only (as the circulation remains near the wingtip). But I did see the Airbus reaching down with a titanium talon, gracefully snatching a whale out of the water (LOL).


text:
What is this strut in biplane rigging, attached only to wires, not bearing any load?
A few biplanes like the Stearman have a strut parallel to the fuselage, halfway along the rigging's landing wires and flying wires, not fastened to the airframe, not bearing any obvious load.  One on each side.  What are they for?  What are they called?
I'd guess that because some of the Stearman's wires are doubled (also unusual?), the strut prevents them from banging into each other and chafing.  But that seems unlikely because their tension is 800 to 1400 pounds, according to page 24 of the Dec. 2007 issue of Vintage Airplane (p. 26 of the pdf).  Even if a maneuver temporarily halved that tension, deflecting one of those by two inches to hit its twin would take tons of force.

(image source: Wikimedia)

It's just a stick set between the flying and landing wires (the "wires" are actually solid stainless steel rods with an almond cross section for streamlining - they are VERY expensive).  Normally they are made from wooden dowel with notches for the wires to fit, retained in the notches by wraps of lockwire, or on fancier biplanes they may be made from aluminum tube with a bullet nose and pointed tail.
They are usually called "wire stays". Their main function is to stop the wires from vibrating in the airflow (they're more or less metal vocal cords), which can create a lot of noise (that's the traditional diving airplane sound effect from the movies, as you can hear hear here, at 1:50:30, in Hell's Angels, one of the earliest sound movies with airplanes). The noise is from the "Wind in the Wires" (the title of a book by WWI pilot Duncan Grinnell-Milne). More importantly, the vibration can also induce fatigue cracking of the streamlined rods over the long term. Linking them together changes the natural frequency of the wires to something much higher than an individual wire, and stops them from vibrating in the airplane's speed range.

Yes, I see how such a stick raises the resonant frequency.  (1) Am I just inattentive to not see it on other biplanes, with similar rigging?  Why not on those as well?  (2) I found a few pre-WWI references to wire stays on airplanes, but it wasn't clear that the term meant these sticks.  Any references for this term?  (fyi "wire stay" in common sailing parlance means a forestay or backstay made of wire instead of solid rod, hemp, etc.;  that's what it sounded like in what I found, the "flying wires" were themselves called "wire stays.")

@CamilleGoudeseune made my own revisions and additions based on your edit suggestions.  Thanks.

@CamilleGoudeseune I would say they are pretty common on biplanes.  I see them more often than not. Like here: https://buildandfly.shop/product/pitts-s1s/ .   They are actually quite important to prevent fatigue cracking at the threads of streamline sold rod wires. The term is one I recall from my own experience around homebuilts over the years and I guess the meaning has changed somewhat in the adoption from the nautical.  I looked around on the web and has a surprisingly hard time finding any direct references.

javelin Strut is a wooden stick connecting the flying wires and landing wires where they cross, at the front of the wing to the matching set of wires at the rear of the wing. It stabilizes the wire sets from excessive movement.

The javelin stick is only attached to the rigging (non-structural).

From review: What is the source of this content?

@user89693 welcome to aviation.stackexchange.com!  Can you provide a source for the quote in your answer?


text:
Is is possible to have an aircraft launched from a submarine or directly from under the water?
There are actually small UAV launched by submerged submarines and projects around submersible aircraft, I'm interested in a view of the current state of launching aircraft from submarines.

Does anything prevent aircraft to be launched and recovered using submarines platform today?

What is the current state of deployment of such technology around the world?

@RonBeyer: I mean today. These submarines are not what I would call indetectable.

I don't think it's possible today. The naval aircraft that are in use today are just too big to store inside a submarine. The F-35 is a VTOL aircraft, but only when very lightly loaded, otherwise it needs a running start. Subs also move on top of the water a lot more than aircraft carriers (not to mention not sticking out as much), which almost necessitates water landings and long recoveries (hoisting). I don't think this can be done with what we have today.

This is a pretty big change in the question; I'm not sure the existing answers are still valid answers to the question in its new form.

@ZeissIkon: I've extended to submersible aircraft, else this is still about submersible carrier, today, as before it was reopened.

Aircraft? Yes. cruise missiles. Direct-launch cruise missiles especially has been widely deployed since the 70s.

Does this answer your question? Has an airplane ever been launched from a submarine?

@Pilothead: Not really, the other question talks about WW2 era or missiles.

@Pilothead: Closely related, but not a duplicate (this one asks if it's possible, the other asks if it's actually been done).

@Sean: Thanks for explaining, but I guess this won't be understood by the usual closists. Don't worry.

The Japanese navy did that in WW2. https://en.wikipedia.org/wiki/I-400-class_submarine

The Regulus missile was a (pilotless) aircraft launched from American submarines in the 1950s -- it in turn was a nuclear armed upgrade of the Hermes, which was a captured, and later copied, German buzz-bomb launched from a deck catapult.
As noted in another answer, the Japanese built a small number of very large submarines with a sealed hangar on the deck; each carried and could catapult launch (as I recall) three Zero or similar aircraft equipped with floats, which would land alongside and be hoisted back aboard.  These subs never saw significant service, as Japan surrendered while the first was on it's first mission near South America.
Modern (nuclear) submarines are highly optimized for submerged operation, and aren't steady enough on the surface to launch and recover piloted aircraft even if modified to carry something like a Harrier or F-35, but there's no reason drones couldn't be launched (brought on deck through the escape trunk, deck hatch, or sail) and, in the case of hovering types, recovered while surfaced.

Interesting. Yes there are drones launched from submarine, though I'm interested in larger aircraft, and perhaps related technologies such as submersible aircraft.

Aren't all cruise missiles pilotless aircraft?

Yep.  And Tomahawks launched from torpedo tubes can give attack subs (Los Angeles class) nuclear capability.  But you generally don't want to recover a Tomahawk at the originating vessel...


text:
What is the shape of the power required curve?
I understand that when flying level, some power is required to maintain altitude, this power amount being:

Normally larger when the speed is larger, this is flying on the forward side of the required power curve.
But below the minimum required power, this amount of power needed to maintain altitude goes down when speed increases. This is flying the backside of the curve.

This can be represented like this:

Being on the backside of the curve means flying in an area of strong instability, possibly reaching the stall point if not managed correctly.
Question: What is the shape of this power required curve for a small GA airplane, and for a large commercial airplane?
I mean is the backside a small portion where it is unlikely to be without obvious pilot mistake? (left hand side below) or is it a large area where it is easy to fall? (right hand side)

No, the left part is instable: if there is a random decrease in speed in the red portion without changing the power setting (power available), the speed will continue to decrease by itself instead of self-correcting as this is the case on the other side. See "low speed" section here.

The shape of these curves (even qualitatively) depends on the aerodynamic characteristics of the aircraft in question, I believe. As such, this will be hard if not impossible to answer generically. If you were asking about a specific aircraft type, one could try to find data for it.

is it not true that the left side of the curve represents a condition where the angle of attack is large enough that part of the lift required to maintain altitude is being generated by the vertical component of the propellor's thrust vector?

@nielsnielsen Not necessarily. The left side of the curve “simply” represents a condition where induced drag (drag due to high lift coefficient = high angle of attack) increases disproportionately with decreasing speed, provided level flight is maintained. For some aircraft, it is possible that the thrust vector is angled upward enough in these conditions to generate a meaningful upward force, but that’s not intrinsic to what the curve represents.

got it, thanks. it's the "backwards" component of the lift vector then, yes?

I suggest reading this bit from MIT.  I'd post  as an answer but my editor skills are lacking in the equation department.

@nielsnielsen Sort of. It’s the backwards component of the total aerodynamic force... the vertical component of which we call lift, and the horizontal (backwards) one drag.

@cpt reynolds, I see it now, thanks for explaining this for me. -Niels

What is the shape of this power required curve for a small GA airplane, and for a large commercial airplane?

The answer depends on the span loading and flight altitude of the aircraft. For most practical cases, the left hand side power curve is more realistic, but it still can be entered if the pilot is unaware of what he/she is doing. Just witness AF447 …
The power curve is the sum of two drag curves, times flight speed:

The induced drag is dominant at low speed and decreases with increasing dynamic pressure, and
the friction (and parasitic and interference) drag grows with increasing dynamic pressure.

Below I have plotted the theoretical power curves for a small GA airplane at sea level. The dashed lines show the power curve if no flow separation would happen.

Aircraft with low span loading will exhibit low induced drag, so the friction drag (zero lift component) will become dominant soon. The higher the airplane flies, the more the available power is reduced and the induced drag is increased, so the power curve will shift to something resembling your right plot. The point splitting the left side of the curve from the right side is the point of minimum power. Where is this point for actual configurations?
We can calculate the lift coefficient at minimum power in order to know where the speed range of the backside of the curve starts. In this answer, I derived this already, so here is only the result:
$$c_{L_{min.\:power}} = \sqrt{\frac{2-n_v}{n_v+2}\cdot c_{D0}\cdot\pi\cdot AR\cdot\epsilon}$$
The symbols are:
$\kern{5mm} c_L \:\:\:$  lift coefficient
$\kern{5mm} n_v \:\:\:$  thrust exponent, as in $T = T_0\cdot v^{n_v} $
$\kern{5mm} c_{D0} \:$  zero-lift drag coefficient
$\kern{5mm} \pi \:\:\:\:\:$  3.14159$\dots$
$\kern{5mm} AR \:\:$  aspect ratio of the wing
$\kern{5mm} \epsilon \:\:\:\:\:\:$  the wing's Oswald factor, normally between 0.8 and 1.0
Now let's input the values for a glider ($n_v$ = -1):
$$c_{L_{min.\:power}} = \sqrt{3\cdot 0.00935\cdot\pi\cdot 21.43\cdot 0.98} = 1.36$$
So the minimum power speed for the ASW-20A is very close to its stall speed. Falling into the backside is practically equivalent with stalling.
Now the values for a jet fighter ($n_v$ = 0):
$$c_{L_{min.\:power}} = \sqrt{0.0172\cdot\pi\cdot 2.45\cdot 0.76} = 0.317$$
So the Starfighter pilot is on the backside of the curve until he accelerates beyond 191 m/s or 371 knots (at maximum take-off mass). That is already Mach 0.54 at sea level (and more the higher you go), and explains why the Starfighter prefers to be flown fast. Its best climb speed is at Mach 0.9!
Since you asked about a commercial airplane, here we go:
$$c_{L_{min.\:power}} = \sqrt{1.67\cdot 0.01277\cdot\pi\cdot 9.58\cdot 0.74} = 0.687$$
This is for the clean configuration of course and falls between the glider and fighter values. The numbers for a GA aircraft are a little higher (around $c_L$ = 1) due to the piston engine, with a higher Oswald factor due to an unswept wing and a somewhat lower aspect ratio. Commercial aircraft prefer to cruise close to the minimum drag point, which for this example is at $c_{L_{min.\:L/D}}$ = 0.532, so at altitude their operating point is already quite close to the backside range. In contrast to that, a GA aircraft in cruise will fly low (no pressurisation) and much faster that at its minimum power, so its cruise point will be far to the right of the backside range, making the power curve look more like your left hand side example.


text:
What was the first commercial scheduled flight to Australia from another continent (except Asia)?
Australia has been a very isolated country, ships being the only possibility to get there from another continent if someone was not too much in a hurry. Aviation did add a new and radically different possibility.

Source
When and how did occur the first commercial scheduled non-stop flight to mainland Australia (country) from mainland Americas, Europe, Africa or Antarctica? I'm excluding overseas islands and Asia which are easier challenges.

@foot, non-stop flights. The idea is also to exclude small overseas islands that may belong to other countries, a 4,000 km flight doesn't qualify :-)

I hear that a lot, that Australia is far away. But it is right outside my door!


text:
Is there any civil aircraft that decelerates with a parachute?
Some previous generations military aircraft decelerate with a parachute to decrease landing distance:

Israel Aircraft Industries Kfir landing with a parachute (source)
It this something found on any civil aircraft today?

Generally speaking, I thought all aircraft decelerated with the deployment of a parachute.  (grin)  Whether military, civilian or experimental.

I assume you don’t include gliders?

This has actually been asked before; See https://aviation.stackexchange.com/questions/24530/do-any-commercial-airline-models-have-a-parachute-at-rear-to-help-in-landings

@Penguin: Good find, let's close this as a duplicate then.


text:
Are piezoelectric energy harvesters too expensive to be used commercially as a power source in drones or small aircraft?
Piezoelectric energy harvesters can draw energy from the mechanical loads and the vibrations in the fuselage/wings/blades of aircraft.
What are the disadvantages of such a system being used as an auxiliary power source if not the main one? Is it not worth the money?

Too heavy too produce meaningful amount of power.

What is too heavy? If you mean the airframe, then what about using them as an auxiliary source to drive smaller electronic components like servos maybe?

Any form of energy harvester in general. You can recover heat from engine exhaust, or you can cover the wings with solar panels. The energy harvested in a few hours simply doesn't worth carrying the harvester around.

Seems like this would conflict with another goal: Minimizing vibration.

Piezoelectric energy harvesters can draw energy from the mechanical loads and the vibrations in the fuselage/wings/blades of aircraft.

Ok, think about this: in a perfect airplane, there would be no vibration. Every erg of energy being used would go into the propulsion. Any vibrations are, by definition, wasted energy.
Think about a specific example. You know the vibrations in a turboprop plane that make it sort of "buzz" inside the fuselage? That's caused by air off the props that hits the fuselage. That air is being pushed by the engine, yet it's not pushing the aircraft forward. That is the definition of wasted energy.
Ok, so real aircraft waste some energy, big deal. But how much? Obviously, the thing is flying, right? So it can't be that much. I mean, if it was 50%, that would be 2000 hp of wind smacking into the fuse - you'd need a parachute, not ear protection! So we're talking about what, 1%? 3%
So that's why we don't use piezos to recuperate. You're trying to collect this tiny bit of power. Even at 100% efficiency, and I'd say 10% is more likely, we're still talking about a tiny fraction of the power you need to do anything.
In fact, the only use of piezos in this role is the exact opposite. The Q400 (and others I assume) power a set of piezos on the fuselage that provide the opposite vibration to the air off the props, and thereby lower cabin noise.

What are the disadvantages of such a system being used as an auxiliary power source if not the main one? Is it not worth the money?

It's not worth the weight.
The power that can be extracted from piezoelectronics is on the order of microwatts (100 uW in the above article). In contrast, light aircraft have their power measured in kilowatts and commercial aircraft reach a megawatt of electrical power.
In other words, it would take 8-16 million of piezoelectronic harvesters to replace the alternator on a small aircraft, and 3-10 billion on a modern airliner. Drones use more power than small aircraft as they've got a lot of electronics.
Piezo harvesting is being developed to power completely unattended tiny sensors that won't have access to any other power source for years. All aircraft, including drones, already have their own power source - the engine - with fuel tanks that get refilled each flight. So power's cheap and available.

the quantity of power (volts times current) produced by flexure of piezoelectrics is very small. You would need a very large number of them to produce useful amounts of power from airframe vibrations.


text:
How are turbine blades overhauled?
How are turbine blades overhauled? What techniques are commonly used and how does it affect the integrity of the blade?

a single blade?

Heres an article on it note: it requires a free registration to read.

I rewrote your question to ask for more specific things. Maybe it will be reopened. I think it’s entirely answerable, but I don’t think you’ll get a step-by-step guide. Feel free to roll back the edit.

TomMcW Thank you ! user3528438 yes a single blade. How can we overhaul it ?

Discs, blisks, and blades are all very expensive components so if they can be salvaged through repair and overhaul programs they usually are. According to this article overhauling a high pressure turbine blade from the CFM56-7BE is 80% cheaper than producing a new one, which is roughly inline with my experience. The actual overhaul process will vary depending on why the item was taken out of service and what condition it is in. There are many companies out there that are built around overhauling various components of gas turbines and many OEMs like RR & Siemens have programs or side businesses for it.
Compressor blades
For a compressor blade a full inspection is required to check it still meets the original specification. This would include at a minimum:

Visual inspection for nicks, scratches, or any other damage
CMM inspection (or equivalent) for shape and size
Weight and balance measurements

If there is any damage to blade it may be possible to repair them through welding or other approved methods depending on the location and severity, but I've never actually come across any company doing so for compressor blades, they're normally discarded.
Turbine blades
All of the above also applies to turbine blades, except that they often can be welded and repaired if they're cracked. They're much thicker and sturdier than compressor blades. If the blade is coated, (pretty much all modern blades are) the coating will have to be removed, replaced and re-inspected for thickness. There will also be a check that all the cooling holes are clear and functional.


text:
What's the exact moment were the spoilers are supposed to be deployed on a A320?
Are they deployed when the levers are pulled back to 'IDLE' or only when pulled back to 'Reverse'?
I still can't figure out, 12 years after, why flight TAM JJ3054 crashed into a gas station and a building, in São Paulo, Brazil. The investigation concluded that the captain pulled the left engine lever to reverse, but "by mistake", left the right one on 'CL'.
For those who don't remember the tragedy: 1- right reverse was pinned due to a malfunction; 2 - It was raining at the Congonhas Intl. Airport at the moment of the crash; 3 - the a320 landed on the touchdown mark on 35L runway ( about 1290 meters long); 4- Left reverse deployed but no spoilers nor hydraulic breaks engaged; 4 - Death toll: 199 souls.
To this day, they can't fully determine whether the captain left the right lever on 'CL' or the FDR displayed, erroneously, 80% of thrust on right engine, when it was supposedly on 'Reverse' position. The pedestal was found among the wreckage, twisted and melted beyond recognition.

Your question seems perfectly legitimate in the title, but you included speculation about other things that could have caused the accident. Thus it was put on hold as opinion-based. I removed the speculative items so that the technical portion of the question can be answered.

@TomMcW Thanks anyway. The speculations included , in my opinion, are necessary for a good brainstorm of the subject matter, since the authorities and the press in general rather conside the pilots as the responsables for the tragedy, wich is not correct. Proofs should have been presented in order to blame the pilots. But the main proof no longer exist. But we have a software controlling an aircraft wich is 100% percent reliable, right? Pilot's families still suffer under the suspicious of a possible human failure wich has never proven to be true. But thanks for the tip I understand the rules.

Problem is, brainstorming is not what the site is about. But you did ask a question than can be specifically answered, as per site rules. The specific conditions that trigger ground spoiler extension are easy to document and they are relevant to explaining the reasoning behind the conclusions made by the investigators.

@TomMcW I understand. And I agree the question he's been properly answered. Best regards

According to the A320 FCOM the ground spoilers are extended full at landing when

both main landing gears have touched down, when:

Ground spoilers are armed and all thrust levers are at idle, or
Reverse is selected (on at least one engine, other thrust lever at idle), if ground spoilers were not armed

The ground spoilers also partially extend (10%) when reverse is selected (on at least one engine, the other thrust lever at or near idle) and one landing gear is compressed. This is to help the other landing gear to touch down, thus triggering full extension.
Here is the flowchart from the FCOM:

source: A320 FCOM
In the case of the TAM accident, this is pertinent to the investigators’ conclusion because the pilots indicated on the CVR that the spoilers did not extend. This gives a clue as to the position of the thrust levers. The spoilers should have extended at touchdown if both levers were at idle or when reverse thrust was selected if the other lever was at or near idle. The fact that they did not extend reveals that one of the levers was not at or near idle.
This might have resulted from the captain using the old procedure for landing with a reverser disabled and he would have had a good reason to do that. The updated procedure, which was to move the levers as if both reversers were working resulted in a slightly longer landing distance than the old one (approx. 55 meters). Knowing he was landing in wet conditions it would be reasonable for him to want all the distance he could get.
It’s also reasonable to conclude he could have left a lever in climb position. The very reason Airbus had changed the procedure, even though it extended landing distance, was because pilots had made that mistake before. In the high-workload conditions at landing pilots were prone to a cognitive error of thinking that they only needed to move one lever because the other reverser was not working. In other words, during the several steps to moving the levers, on one step you move only one of them. When thinking quickly pilots would sometimes do that on the wrong step. On this occasion, combined with the poor runway condition, it resulted in disaster.

Man... That's so surreal to think such an experienced airliner would do something like that. But yeah, I agree that the scenario could lead them to a mistake: poor runway, heavy aircraft, feeling somewhat tight on a (usually) difficult landing , which allows no margin for mistakes, such as Congonhas Intl.;technical limitations (pinned reverse). As to the F/O... In the heat of the moment, he probably wasn't able to see the actual position of the right lever. Panic at the cockpit :=/. Regards

PL at idle is one of several conditions (weight on wheels, N1, wheel speed etc) that have to be satisfied to get ground lift dumpers to come out on airliners.  Reverse isn't required.  Once on the ground, just moving the PL levers back toward TO thrust makes them come back down.


text:
What exactly do "captain", "pilot", "co-pilot" and "first officer" mean?
I know the co-pilot sits beside the pilot. But it's not clear for me, who is the captain and who is the first officer?
And where they are sitting during the flight? Who is in right seat and who is in left seat, and probably who will seat behind the front seats for an aircraft with more than two flight crew?

The term co-pilot has largely fallen out of use in the industry. It’s mostly used nowadays only by the media and public.

Is in jet fighter also use term captain rather then pilot?

Since “captain” is a rank in the armed services, and a different rank between different branches, the pilot would only be called a captain if he/she was actually that rank. In the USAF I believe some pilots are captains. But in the navy they would not be. I’m not real familiar with military terms, so they may still use co-pilot on aircraft that have a two-pilot crew.

Btw, edited your question to read “flight crew.” Cabin crew would be the flight attendants, etc.

Thank @TomMcW for your kindness to correct my question. As not native English speaking, I realize that my English is far from good. That the reason I always appreciated every correction that I believe will help readers to understand.

Capt left, 1st officer or copilot right. On older airlines with a flight engineer, he is behind and is called 2nd officer.
It's the same as a ship.  Capt is boss, 1st officer is second in command, 2nd officer if on board is 3rd in command.
Capt always starts the engines and taxis the airplane since most airliners only have a steering tiller on the left, and FO usually handles radios and checklists, FMS programming etc when on the ground.  FO, if it's his/her turn to fly, only controls the airplane from the start of the takeoff roll until completion of the landing roll.
On a pairing (sequence of trips over 2 or 3 or 4 days), capt and FO normally alternate on each leg of the trip as pilot flying with the other as pilot monitoring.  But as I said, if FO is PF for a particular leg, he/she will still do the radios until the start of the takeoff roll, then takes control of thrust and stick once the capt has lined up, upon which capt looks after comms/FMS/button pushing, until completion of the landing roll, when the FO hands control of the airplane back to the capt and the FO (who only has rudder pedal steering and can't make sharp turns) takes over the radios again.
On an older airliner with a Flight Engineer/Second Officer, that person is type rated on the aircraft as a pilot but never actually flies the plane until he/she moves up to right seat as FO.  So in the old 3 crew days a new pilot would be hired as a Flight Engineer in an airline with only 3 crew aircraft and might go several years in the 3rd seat before actually flying the plane, or if upgrading from 2 crew to 3 crew in the same airline.
Up until the 60s you also sometimes had a 4th crew, a Navigator.  Don't think there were any Navigators left by 1970.

Just a note to point out that on some airlines, especially smaller ones and freight carriers, the Flight Engineer/Second Officer usually was not type rated in the airplane. Indeed they often did not have a pilot's license, but of course they had a flight engineer's license. The two 747 carriers I flew for, one a freight carrier the other a passenger carrier used this system, and additionally they required the flight engineers to have A&P licenses. The flight engineers were almost always former military flight engineers.

What is number of cabin crew in 747?

@AirCraft Lover - The cabin crew look after the passengers, the flight crew fly the aircraft

@AirCraftLover The early models of the 747 had a cockpit crew of three; all recent versions (and, basically all modern passenger planes) have two, because the computers now do almost all the work that the Flight Engineer used to do.

@Terry yes I forgot to mention that and in fact an old chum was a non-pilot FE with a charter airline into the early 90s.  They started to replace them with pilots about that time and offered FE crew who had the base requirements type ratings, but my friend didn't and left the company.

Why don't they ever switch seats, e.g. so that the FO can taxi? i.e. I wonder why the Capt is always on the left?

An FO upgrading to Capt may do a number of trips from the left seat while being evaluated by a training Capt in the right, prior to formally being made Capt.  And I have heard the military does that (whoever is PF sits left seat) but not sure.

@JohnK I wonder if the reason for starting to replace FEs with pilots in the early 90s was the FEs were well into the process of being phased out entirely by that point and they were trying to provide them a path to still have a job as types that required an FE were being retired.

Yes my chum more or less said that was the reason.

@AirCraftLover That's a separate question. Consider posting it as a general question rather than in a comment, something like how is the number of the cabin crew determined. The last 747 pax airline I flew for scheduled 14 flight attendants into every flight, but the regulatory requirement at the time was only 12 for the typical seating configuration of around 480 pax.

@JohnK Concerning an FO upgrading to captain, in the U.S. there's a regulatory requirement (no "may" about it) for a specified number of hours and landings in the left seat while a check airman is in the right seat. The requirement is referred to as IOE, initial operating experience.

@JohnK Just a note, 747s have a tiller on both the left and right side and thus can be taxied from either side. Whether they do or not is a matter of airline policy and the captain's preference. Personally, it if was the FOs leg, I had them do the taxiing.

@Terry so does the C series/A220.

You might mention that on long haul flight with one captain and two FO’s there can be an FO in the left seat while the captain is on rest

@DaveGremlin, sorry for my mistake. What I mean should be cockpit crew.

Note that in non-airline business or commercial aviation the captain and co-pilot/co-captain/first-officer titles are titles of legal responsibility corresponding to the PIC/SIC roles. These do not necessarily imply which seat the pilot will sit in or what PF/PNF responsibilities he or she will assume. When I am assigned a trip as PIC, I frequently fly with type-rated FO or Captains; our GOM allows these "FOs" to sit left seat on 91 and 135 legs respectively. We frequently switch seats. I am far more comfortable acting as PNF from the right seat than the left.

just pointing out in that the “capt only taxing/engine starting” and “fo does radio only on ground” is slowly getting phased out in airlines where the plane technically allows it (ie. two tillers). This policy creates a training unbalance where a newly promoted capt now taxies the aircraft for the first time in his life, alongside an fo that never taxied. Better to have the fo learn to taxi while sitting next to an experienced captain in the left, before the upgrade

The title of Captain designates that he(she) has final authority during the flight, and First Officer is assisting.   Ultimately, a Captain may make critical decisions regarding the flight.   In practice and ideally, the Captain and FO will work collaboratively, and there won't be a need to "pull rank".
The terms Pilot and Co-Pilot are actually rarely used in commercial aviation anymore.  Instead, the terms "Pilot Flying" (PF) and "Pilot Monitoring" (PM) are used to designate who has actual hands on the controls, and who is overseeing the flight and providing guidance.  The PM also typically handles tasks like radio traffic or setting up the computer (FMS) with proper settings.

Seems that Captain and First officer is definetely different. As I just watch a video by a captain discussing about a topic What pilot will do if there is an engine failure. He said, "The captain will talk to the first officer...". That clear that captain is not first officer.

@AirCraft Lover - Captain and First Officer are two distinct people, both are pilots.  PF and PM are roles that either the Captain or the First Officer will assume during the flight.  Usually the Captain decides who is to be PF and who is PM.  In fixed wing aircraft the Captain usually sits on the left and the FO on the right (in rotorcraft the Captain usually sits on the right for some reason).  The Captain has four gold stripes on his sleeve, the FO has three.  Co-pilot isn't a term you hear much these days, though I don't fly professionally, so don't take my word for it

"The titles of Captain and First Officer designate who has final authority during the flight." - This sentence is unclear, because it kind of sounds like you're saying that the title "Captain" refers to the person who has final authority, and the title "First Officer" also refers to the person who has final authority. I suggest editing this answer to clearly state that the captain has final authority and the first officer does not.

"The title of Captain designates that he(she) has final authority during the flight, and First Officer is assisting." So if the flight crew consists of two captains, instead of a captain and a first officer, then who has final authority?

" So if the flight crew consists of two captains, instead of a captain and a first officer, then who has final authority? "  I saw a YouTube video from Mentour Pilot on this.  He says in most cases this is decided by the airline before the crew reports to work.  The pilot in command will be the person designated explicitly seniority in the airline or some other process that might rotate the roles.  If this isn't made explicit by the airline then there will have to be a discussion between the two captains on who is in charge, as deciding that in the middle of an emergency could be lethal.

A pilot is someone who takes direct part in flying an aircraft by manipulating flight controls.
A captain is a person who can (in the sense of is capable of and legally permitted to) act as a pilot, and who has been hired or promoted by their employer to the rank of captain. They are normally the highest-ranking working employee of the operator aboard the airplane, though exceptions exist. They can typically be recognized by having four gold bars on their shirt shoulders.
A first officer is a person who can (in the sense of is capable of and legally permitted to) act as a pilot, and who has been hired or promoted by their employer to the rank of first officer. It is the rank below captain. They can typically be recognized by having three gold bars on their shirt shoulders.
As already stated, the term co-pilot isn't widely (if at all) used in commercial aviation. Both pilots in the cockpit of a modern airliner are fully qualified pilots, and the terminology has been changed to reflect this fact.
Older airplanes typically had a flight engineer in the cockpit as well; this is a flight crew position, but it is a person that does not directly take part in directing the path of the airplane (it is a non-flying flight crew position). Older yet, they also had a separate position for a navigator, who would tell the pilots where to go. In modern airliners, both of these positions have been replaced by computers.
To answer what you didn't ask, there is another three important terms to know: Pilot Flying, Pilot Monitoring and Pilot In Command.
The Pilot Flying is the pilot that is directly operating the airplane by making control inputs to control the direction in which the airplane is going.
The Pilot Monitoring (or Pilot Not Flying) is the pilot that is keeping an eye on the Pilot Flying, and looking at the instruments, to make sure that the flight is proceeding safely. They will also usually do things at the request of the Pilot Flying. For example, the Pilot Flying may call out for a specific flap setting, or for the landing gear to be raised or lowered, or something similar; the Pilot Monitoring would usually be the one making those airplane configuration changes. The Pilot Monitoring may also be handling radio communications with Air Traffic Control.
Pilots will typically alternate who acts as Pilot Flying and who acts as Pilot Monitoring. This can even change at a moment's notice in the middle of the flight, but there will always be one pilot acting as Pilot Flying and one pilot acting as Pilot Monitoring, and there will always be a clear understanding among all involved who is acting in which role. Accidents have happened when it was not clear in the cockpit who was acting as Pilot Flying and who was Pilot Monitoring, or when the roles became intermingled by one pilot acting in parts of both roles.
The Pilot In Command is the person who is ultimately responsible for the safety of the flight. They can be regarded as the boss in the cockpit, but thanks to the advent of Cockpit Resource Management (CRM), reality is that they are more of a leader than a boss. A good pilot, whether or not they are PIC, will seek the input of their colleagues as much as possible. The PIC will typically be a captain. There is no requirement that at any given time the Pilot In Command is the Pilot Flying. (Some operators may however require in their operational procedures that, say, the PIC, or a captain, is the one performing certain maneuvers, and some aircraft may not be equipped to perform all maneuvers from either seat.)
With these (rough) definitions, we can see that there is no necessary contradiction in something like a flight crew consisting of multiple captains (with a clear understanding of who is Pilot Flying and who is Pilot Monitoring, as well as who is Pilot In Command); or a person who is a captain acting as Pilot Monitoring while another person in the cockpit (or possibly even not in the cockpit) is Pilot In Command, and quite possibly a person who is a first officer acting as Pilot Flying.

I think your last paragraph is very important: on long-haul flights, it is entirely possible that, for example, the pilot-in-command is not even in the cockpit (or even awake), he may be in the Crew Rest Area, taking a nap. It is possible that two first officers are in the cockpit and the captain is sleeping. Or, two captains are in the cockpit, but neither of them is pilot-in-command, because the PIC is a third captain with more experience, who is currently resting. Also interesting: during the QF32 incident, there were no less than 5 qualified pilots inside the cockpit.

In aircraft,they must have a nominated pilot who is the incharge of the aircraft, this pilot is the Captain. A newly qualified airline or private jet pilot is allocated the rank of “First Officer” then later “Senior First Officer” before they take a “Command Course” after which they can become a Captain.
The first officer is the second pilot (also referred to as the co-pilot) of an aircraft. The first officer is second-in-command of the aircraft to the captain, who is the legal commander. In the event of incapacitation of the captain, the first officer will assume command of the aircraft.

It's possible to have a flight crew consisting of multiple captains. Captain is a rank, not a position.

Captain is absolutely a position. It's also a rank! Complexities abound.

@Lightness I think A CVn's point was that, while it's usually the case, it's not always true that the guy in the right seat is a First Officer. Sometimes both seats are occupied by Captains. On U.S. carriers, generally both seats will never be operated by FOs (augmented operations require at least 2 Captains,) though 2 FOs + 1 Captain appears to be possible in Europe (AF447's flight deck was occupied by 2 FOs when things went awry, for example, and the only Captain on board was in crew rest.)

@LightnessRacesinOrbit Not really. Pilot In Command is a position. So is Pilot Flying and Pilot Monitoring, respectively. There is no contradiction in having a rank of Captain, being Pilot Monitoring, and not being Pilot In Command, all at the same time. It might be somewhat unusual, but there is no contradiction.

@aCVn Exactly what I mean!

@reirab Yes, exactly.

Job... Pilot flies the airplane, co-pilot helps by doing radios and knobs and switches. Can sit in either seat.
Rank... Captain is usually the senior person of the two, and is basically the decision-maker. Is seen as a more prestigious and higher-paid job then First Officer. Conventionally sits on the left (but there is no legal requirement for this). Thye Captain is also the 'commander' of the airplane, which is a legal position for "if it goes wrong, the buck stops here".

You make it sound like there's a clear distinction between "flying the airplane" and "doing radios and knobs and switches"...

"Pilot flies the airplane, co-pilot helps by doing radios and knobs and switches." Both pilots take turns flying the airplane (i.e. manipulating the flight controls.) Perhaps you're thinking of the distinction between "pilot flying" and "pilot not flying" or "pilot monitoring?"


text:
Why did this old Japan Nakajima J1N airplane use a Yagi rather than a parabolic antenna?

Picture source.
As per my understanding, a Yagi antenna is a directional antenna with limited gain, which it broadcasts or receives the microwave signal to and from the front side. It can only receive signal if the transmitting antenna is not exactly in front of it, or can receive with limited/very limited quality, depending on the direction. Parabolic, however, has better reception than Yagi.
My question is, why did this old Japan Nakajima J1N airplane use a Yagi rather than a parabolic antenna?

Wouldn't parabolic antenna be impractically huge? They worked with relatively low frequencies back then.

But normally used by airplane, especially civil. I am not sure for fighter jet. The parabolic antenna is located in the nose.

Note that there is a relationship between radio-wavelength and antenna-dimensions. I'am not an RF engineer, but I guess the wavelength used in the J1N's radar doesn't allow for parabolic antennas. Checkout the Wikipedia article on the german Berlin radar set of WW2. While the predecessor, operated with wavelengths in the tens of centimeters, the Berlin set operated with 9 cm waves. The article notes, that this allowed to shrink the antenna by a factor of 7 in size, thus allowing to place a parabolic antenna behind an aerodynamic fairing.

First, both parabolic & Yagi antennas are "directional" in that their main lobe is designed to have high gain in a limited direction. this is because all antennas have to trade the width of their main beam(s) with the amount of gain in that beam. you can either put a little power everywhere or a lot of power in one direction.
that being said the picture you show is also from wikipedia. From that Yagi antenna article

The Yagi was first widely used during World War II for airborne radar sets, because of its simplicity and directionality

the subtext on the photo reads:

A Nakajima J1N1-S night fighter with quadruple Yagi radar transceiver antennas

Reading through the J1N article it appears these were used for night surveillance and intercept. Much like modern fighters with radars antennas in the front, the likely use was for tracking or targeting targets - probably B29's. With the Yagi (or any highly directive design) the radar can 'see farther' since it has high gain in the forward direction.
With 4 antennas with their beams pointed in slightly different directions their coverage would have been a bit wider (both in azimuth and elevation) for searching.

It appears these were used for night surveillance and intercept. Interesting.

Note that the assertion "It can only receive signal if the transmitting antenna is not exactly in front of it" is wrong. The most sensitive direction for receiving is in fact exactly in front of the antenna, so if the incoming beam is directly in line with the yagi shafts, the maximum signal strength will be received.
A parabolic antenna would be bigger across than the width of the plane's fuselage, causing a huge amount of (unnecessary) drag.